Graphite is the most common anode material used to make lithium ion batteries. It is usually coated on a copper substrate or foil, but other lithium inactive metals may be used. Graphite offers a reversible capacity of about 370 mAh/gram, and suffers an irreversible capacity loss of about 5% to building a solid electrolyte interphase (SEI) layer. Recently, higher capacity anode materials have been introduced that could greatly increase the specific capacity of the lithium ion battery. For example, amorphous silicon can provide as much as 3500 mAh/gram (Obrovac M N and Krause L J, 2007. Reversible cycling of crystalline silicon powder. J. Electrochem. Soc. 154: A103-A108).
Since anode materials used in lithium ion batteries do not contain lithium initially, cathode materials usually supply all of the lithium used in battery cycling and irreversible cycle loss (IRCL). Unfortunately, silicon exhibits an IRCL of up to 25%. This would mean that 25% of the cycle able capacity of the battery would become unavailable and the expensive and heavy cathode would be underutilized.
There have been attempts to add extra lithium to anode material by: a) adding a thin layer of lithium metal to the cell; b) adding lithium to the anode active material by electrolysis in a non-aqueous and dry environment; c) dispersing lithium into the anode material as in stabilized lithium metal powder, or SLMP (FMC Corporation, Philadelphia, Pa.); and d) adding lithium donating substances to the battery electrolyte during assembly. U.S. Pat. No. 8,133,374 B2 is referenced here as a partial review of some of these methods. U.S. Ser. No. 14/590,573 filed Jan. 6, 2015, published as US Publication No. 2015019184 on Jul. 9, 2015 entitled Method of Alkaliating Electrodes by Grant et al., is incorporated by reference in its entirety and for details of a process and an apparatus for electrochemical lithiation.
For anode rolls in commercial environments, it is desirable that some portion of substrate be uncoated in order to accommodate subsequent cell assembly methods, such as tab welding, slitting, or for other purposes. An anode roll is defined as an anode material which is of sufficient length to roll. FIG. 1 shows edge view of a common anode substrate 101 with a coating 102 where bare copper areas are present on both faces of the substrate in order to facilitate a spiral wound cell packaging technique. In another situation, the bare copper may be exposed on one or both edges 103 of the roll to accommodate the welding of cells constructed with cut, stacked electrode sheets. In yet another case, it may be desirable to use wide anode rolls (e.g. 30-60 cm) for efficient production of small cells for consumer electronics devices. In such a case, interior surfaces of these larger anode rolls would contain many bare copper areas in rows or columns, and the exterior or edges might also need to be protected. In all these cases, any bare substrate area needs to be protected from lithium metal buildup during the electrochemical lithiation of the anode roll. If these and other configurations could be processed roll to roll, then mass production could be realized.
U.S. Pat. No. 8,133,374 B2 teaches a way to use electrolysis to lithiate an anode substrate where a reference electrode detects areas of bare copper in order to “turn off” the current while the bare copper area is passing. It does not teach how this can be done on an anode coated on both sides, and hence is impractical for most commercial purposes in which anode rolls are double-sided. It also does not teach how to avoid lithium plating or dendrite buildup on the edges of a substrate. Since field strength concentrates on the substrate edges in an electrolysis bath, U.S. Pat. No. 8,133,374 B2 is impractical in that it does not protect the edges.